Electronic devices include circuitry formed within semiconductor substrates. This circuitry includes a variety of components, including transistors. Such circuitry also includes metal lines and contacts that connect the components in the desired manner in order to form a functional circuit. Fabrication of such circuitry is often done layer upon layer.
For example, a semiconductor substrate may include a number of gate terminals for transistors. The regions of the substrate adjacent to the gate terminals are then doped to form source and drain terminals for a complete transistor. The gate terminals are then surrounded by an interlayer dielectric layer. Holes are then formed through the interlayer dielectric layer extending down to the gate device as well as the doped regions of the substrate. These holes are then filled with a metal material that forms contacts to the gate devices and doped regions. These contacts allow for electrical connection to other layers of circuitry.
In some cases, the contacts that connect through the interlayer dielectric layer to the doped regions of the substrate are formed in two layers while the contacts that connect to the gate devices are formed with only one layer. The holes for both layers of the contacts to the doped regions and the holes for the one layer of contacts to the gate devices are formed using separate masks, for a total of at least three masks. It is desirable to optimize the placement of features on these masks, particularly in cases where the circuitry is relatively congested.